The invention relates generally to power-driven conveyors and more particularly to spiral conveyors in which a conveyor belt is positively driven in a helical path around a rotating drive cage.
Positively driven spiral systems, in which drive structure on the outside of a rotating cage engages structure on the inside of a conveyor belt, have been used to convey articles, such as foodstuffs and other materials, through cooled or heated environments. Spiral conveyors, in which a conveyor belt follows a helical path winding around a central tower, drum, or cage, are used in freezers and ovens to provide a long conveying path with a small footprint. Cage bars extending from the top of the cage to the bottom are spaced apart circumferentially and form the outside of the cage. Cage-bar caps made of a plastic material cover the metal cage bars. Ridges on the cage-bar caps form drive structure that drives the belt. Because there is positive engagement between the regularly spaced drive structure on the cage and regularly spaced edge structure on the inside edge of the belt, there is no slip as in overdrive spiral systems. No additional tensioning is needed and frictional losses are less. But one problem with positively driven spiral systems is in cleanly engaging the belt with and disengaging it from the drive structure on the cage.
In prior attempts to help solve that problem, cage-bar caps 60, as shown in FIG. 6, were used at the entrance of the conveyor belt onto the rotating cage with alignment and guide features, such as a bump 62, that help guide the belt rows 63 into engagement with the drive surfaces 64 on the cage bars 66. Because the alignment and guide features make the entrance portion 60 of the cage-bar caps different from the much longer main portion of the cage-bar caps, it's more economical to have separate main portions 68 and entrance portions 60. The entrance cage-bar cap normally abuts the main cage-bar cap at a seam 70. But, when the spiral conveyor is operated in a freezer, the cage-bar caps 60, 68 contract and separate to form a gap 72, as shown in FIG. 7. The gap can catch on the belt's edge structure and hinder the belt's advancement vertically along the cage-bar caps.